This disclosure relates to polymer films, and in particular to amorphous polymer films useful for the manufacture of capacitors.
Electrostatic film capacitors with high volumetric energy density, high operating temperature, and long lifetime are critical components for pulse-power, automotive, and industrial electronics. Capacitors are essentially energy-storing devices having two parallel conductive plates separated by a thin layer of an insulating (dielectric) film. When a voltage is applied across the plates, the electric field in the dielectric displaces electric charges, and thus stores energy. The amount of energy stored by a capacitor depends on the dielectric constant and breakdown voltage of the insulating material, and the dimensions (total area and thickness) of the film, such that in order to maximize the total amount of energy that a capacitor can accumulate, the dielectric constant and breakdown voltage of the film are maximized, and the thickness of the film minimized. Because the physical characteristics of the dielectric material in the capacitor are the primary determining factors for the performance of a capacitor, improvements in one or more of the physical properties of the dielectric material in a capacitor can result in corresponding performance improvements in the capacitor component, usually resulting in performance and lifetime enhancements of the electronics system or product in which it is embedded.
Electrostatic film capacitors made from biaxially-oriented poly(propylene) (BOPP) have been used in applications requiring a low dissipation factor, high insulation resistance and low dielectric absorption, such as in electrical appliances, electronic equipment, oven and furnaces, refrigerators, automobiles, and home appliances. The low dielectric constant (Dk), which is about 2.2, and the maximum service temperature of about 100° C., limits the use of these capacitors in applications requiring high operating temperatures and/or high energy densities. Poly(carbonate) (also known as polycarbonate, or PC) films have a higher dielectric constant than BOPP films (about 3.0) and a higher maximum service temperature of about 125° C.
There accordingly remains a need in the art for new films and methods for their manufacture that can produce films of very high purity and with excellent electrical properties, in particular high breakdown strength, and high dielectric constant. It would be a further advantage if such films could operate at higher temperature than BOPP films. There remains a further need for efficient methods for producing such films that are amendable to industrial scale processes. It would be further advantage if such methods were environmentally friendly.